ESTRO 2022 - Abstract Book

S824

Abstract book

ESTRO 2022

adverse events. Several studies suggested that BC cells can be more sensitive to high doses administered in short intervals. Preoperative robotic stereotactic radiosurgery (prRS) followed by BCS may yield potential advantages in selected patients. An exploratory phase II study (ROCK trial – NCT03520894) was conducted in our institution. Materials and Methods Women with histologically proven unifocal invasive hormonal receptors positive, HER2 negative BC, sized less than 25 mm, with negative clinical nodal status, aged 50+ and eligible for BCS were enrolled. Fiducial markers were introduced in peri/intralesional position. Magnetic resonance imaging (MRI) was used in addition to standard CT-based planning. Patients received 21 Gy in single fraction with CyberKnife ® followed by BCS two weeks after prRS. The primary endpoint was the acute skin toxic effect rate. Secondary objectives were the pathological response rate and late adverse events. Echocardiography and spirometry were performed before prRs and yearly thereafter. Translational research was conducted to identify correlations between radiogenomic, immunological and biochemical biomarkers with treatment-related response and toxicity. Results From August 2018 to September 2021, a total of 70 patients were screened on mammography; 29 of them were eligible following inclusion criteria. Of those, seven were excluded due to multiple foci disease at basal MRI, and 22 patients were successfully treated. All required dosimetric parameters were met in all patients, as well as normal tissue constraints. Median age at diagnosis was 68 years (range 50-86) and median tumor size was 13 mm (range 7.5-25). All treated patients received surgery within 14 days from prRS without any delay or complication. No patients experienced acute skin toxicity of grade (G) 2 or higher, only one patient had a G1 erythema one month after BCS. According to Chevallier’s classification, two patients had a pathological complete response (pCR). At a median follow up of 18 months, no patients experienced locoregional recurrence or distant metastases. No clinically meaningful changes were observed regarding left-ventricular ejection fraction, FEV1 or DLCO. Conclusion At a median follow up of 18 months, the ROCK trial showed that single dose prRS is a feasible technique in selected BC patients with a good safety profile and encouraging activity. This new approach in BC management warrants further investigations. 1 National Institute of Oncology, Center of Radiotherapy, Budapest, Hungary; 2 Semmelweis University, Department of Oncology, Budapest, Hungary Purpose or Objective To report the 20-year results of a randomized study comparing the survival and cosmetic results of breast-conserving treatment with partial breast irradiation (PBI) or conventional whole breast irradiation (WBI). Materials and Methods Between 1998 and 2004, 258 selected patients with pT1 pN0-1mi, Grade 1-2, non-lobular breast cancer without presence of extensive intraductal component and resected with negative margins were randomized after breast-conserving surgery to receive 50 Gy WBI (n=130) or PBI (n=128). The latter consisted of either 7 x 5.2 Gy high-dose-rate (HDR) multicatheter brachytherapy (BT; n=88) or 50 Gy electron beam (EB) irradiation (n=40). Results At a median follow-up time of 17 years (range: 18 to 254 months) the 20-year actuarial rates of local and regional recurrences were 9.6% versus 7.9% (p=0.59), and 4.5% versus 5.7% (p=0.56) in PBI and WBI arms, respectively. There was no significant difference in the 20-year probability of overall survival (59.5% vs. 59.7%), cancer-specific survival (92.6% vs. 88.1%), and disease-free survival (79.7% vs. 78.3%), either. The rate of excellent/good cosmetic results was 79.2% in the PBI, and 59.5% in the control group (p=0.0007). Conclusion PBI delivered by interstitial HDR BT or EB for a selected group of early-stage breast cancer patients produces similar 20- year results to those achieved with conventional WBI. Significantly better cosmetic outcome can be achieved with carefully designed HDR multicatheter implants compared with the outcome after WBI. Financial support from the Hungarian Thematic Excellence Programme (TKP2020-NKA-26) is greatly acknowledged. OC-0933 Breast conservation with partial or whole breast irradiation: 20-year results of a randomized study C. Polgar 1,2 , T. Major 1,2 , Z. Takacsi-Nagy 1,2 , J. Fodor 1

OC-0934 Outcomes of the EORTC 22922/10925 randomised trial according to the technique for nodal irradiation

O. Kaidar-Person 1 , C. Fortpied 2 , S. Hol 3 , C. Weltens 4 , C. Kirkove 5 , V. Budach 6 , K. Peignaux-Casasnovas 7 , F. van der Leij 8 , E. Vonk 9 , M. Valli 10 , N. Weidner 11 , M. Guckenberger 12 , E. Koiter 13 , A. Fourquet 14 , H. Bartelink 15 , H. Struikmans 16 , P. Poortmans 17 1 Sheba Medical Center, Radiation Oncology, Ramat Gan, Israel; 2 European Organisation for Research and Treatment of Cancer (EORTC), Headquarters, Brussels, Belgium; 3 Institute Verbeeten, Radiation Oncology, Tilburg, The Netherlands; 4 University Hospital Leuven, Radiation Oncology, Leuven, Belgium; 5 University Hospital Saint Luc, Radiation Oncology, Brussels, Belgium; 6 Charité–Universitaetsmedizin Berlin, Radiation Oncology, Berlin, Germany; 7 Centre Georges François Leclerc, Radiation Oncology, Dijon, France; 8 University Medical Centre Utrecht, Radiation Oncology, Utrecht, The